Generating Artificial Pulse

ABSTRACT

In order to produce a pulsatile blood flow pattern that includes time periods of relatively high blood flow rates and time periods of relatively low blood flow rates, the operating speed of a blood pump can be selectively controlled to produce an operating speed pattern that includes time periods of relatively high rotation speeds and periods of relatively low rotation speeds. For example, the blood pump is rotated at a first speed for a first period of time. The speed of the blood pump is then decreased from the first speed to a second speed and is operated at the second speed for a second amount of time. The speed of the blood pump is then decreased to a third speed for a third amount of time. If desired, the operating speed pattern can be repeated to continue the pulsatile blood flow pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of Ser. No. 13/926,044 filedJun. 25, 2013; which is a Divisional of Ser. No. 13/241,831 filed Sep.23, 2011 (now U.S. Pat. No. 8,506,471); which claims the benefit of U.S.61/386,018 filed Sep. 24, 2010. The full disclosures which areincorporated herein by reference in their entirety for all purposes.

FIELD

This description relates to generating an artificial pulse.

BACKGROUND

Ventricular assist devices, known as VADs, are types of blood pumps usedfor both short-term and long-term applications where a patient's heartis incapable of providing adequate circulation. For example, a patientsuffering from heart failure may use a VAD while the patient awaits aheart transplant. In another example, a patient may use a VAD while thepatient recovers from heart surgery. Thus, a VAD can supplement a weakheart or can effectively replace the natural heart's function. VADs canbe implanted in the patient's body and powered by an electrical powersource outside the patient's body.

SUMMARY

In one general aspect, a continuous flow blood pump can be operated toprovide pulsatile blood flow. The motor speed for the pump can bemodulated in a repeating cycle that includes a sequence of two or morespeed levels. Operation of the pump can produce pressure changes thatimitate a rate of pressure change of a natural physiologic pulse.

In another general aspect, pumping blood in a pulsatile manner includesoperating a blood pump at a first speed for a first period of time,reducing the speed of the blood pump from the first speed to a secondspeed, operating the blood pump at the second speed for a second periodof time, reducing the speed of the blood pump from the second speed to athird speed, operating the blood pump at the third speed for a thirdperiod of time, and increasing the speed of the blood pump from thethird speed to the first speed.

Implementations can include one or more of the following features. Forexample, increasing the speed of the blood pump from the third speed tothe first speed includes increasing the speed of the blood pump from thethird speed to a fourth speed, operating the blood pump at the fourthspeed for a fourth period of time, and increasing the speed of the bloodpump from the fourth speed to the first speed. The second period of timeis longer than a sum of the first period of time and the third period oftime. Operating the blood pump at the first speed, reducing the speed ofthe blood pump from the first speed to the second speed, operating theblood pump at the second speed, reducing the speed of the blood pumpfrom the second speed to the third speed, operating the blood pump atthe third speed, and increasing the speed of the blood pump from thethird speed to the first speed comprise a cycle, and pumping blood in apulsatile manner further includes repeating the cycle. The duration ofthe second period of time is greater than half of the duration of thecycle. Operating the blood pump at the second speed for the secondperiod of time includes operating the blood pump to produce a blood flowrate that has a predetermined relationship relative to an average bloodflow rate for the cycle. Operating the blood pump at the second speedfor the second period of time includes operating the blood pump toproduce a blood flow substantially the same as the average blood flowrate for the cycle.

One or more of reducing the speed of the blood pump from the first speedto a second speed, reducing the speed of the blood pump from the secondspeed to a third speed, and increasing the speed of the blood pump fromthe third speed to the first speed includes one or more of a step-wisereduction in speed and a curvilinear reduction in speed. Operating theblood pump at the second speed includes operating the blood pump at thesecond speed during at least a portion of a contraction of a ventricleof human heart that is in blood flow communication with the blood pump.Pumping blood in a pulsatile manner also includes determining, based ona relationship between a speed of the blood pump and a power consumptionof the blood pump, a synchronization between operating the impeller atthe second speed and contraction of a ventricle of a human heart that isin blood flow communication with the blood pump. A generated pulsatileblood flow includes a temporal rate of change of blood pressure thatapproximates a temporal rate of change of blood pressure of aphysiologic pulse. One or more of reducing the speed of the blood pumpfrom the first speed to a second speed, reducing the speed of the bloodpump from the second speed to a third speed, and increasing the speed ofthe blood pump from the third speed to the first speed includesgenerating a drive signal at a first time to produce a correspondingchange in operating speed at a desired time. The second period of timeis greater than the first period of time.

In another general aspect, a blood pump controller includes a waveformgenerator to generate a waveform for operating a blood pump, and a drivewaveform transmitter to supply the generated drive waveform to the bloodpump. The generated waveform is configured to operate a blood pump at afirst speed for a first period of time, reduce the speed of the bloodpump from the first speed to a second speed, operate the blood pump atthe second speed for a second period of time, reduce the speed of theblood pump from the second speed to a third speed, operate the bloodpump at the third speed for a third period of time, and increase thespeed of the blood pump from the third speed to the first speed.

Implementations can include one or more of the following features. Forexample, increasing the speed of the blood pump from the third speed tothe first speed includes increasing the speed of the blood pump from thethird speed to a fourth speed, operating the blood pump at the fourthspeed for a fourth period of time, and increasing the speed of the bloodpump from the fourth speed to the first speed. The second period of timeis longer than a sum of the first period of time and the third period oftime. Operating the blood pump at the first speed, reducing the speed ofthe blood pump from the first speed to the second speed, operating theblood pump at the second speed, reducing the speed of the blood pumpfrom the second speed to the third speed, operating the blood pump atthe third speed, and increasing the speed of the blood pump from thethird speed to the first speed comprise a cycle, and wherein thegenerated waveform is configured to repeat the cycle. The duration ofthe second period of time is greater than half of the duration of thecycle. Operating the blood pump at the second speed for the secondperiod of time includes operating the blood pump to produce a blood flowrate that has a predetermined relationship relative to an average bloodflow rate for the cycle. Operating the blood pump at the second speedfor the second period of time includes operating the blood pump toproduce a blood flow substantially the same as the average blood flowrate for the cycle.

The generated waveform is configured to change the speed of the bloodpump via one or more of a step-wise change in speed and a curvilinearchange in speed. The generated waveform operates the blood pump at thesecond speed during a contraction of a ventricle of a human heart thatis in blood flow communication with the blood pump. The blood pumpcontroller further includes a processor configured to determine, basedon a relationship between a speed of the blood pump and a powerconsumption of the blood pump, a synchronization between operating theblood pump at the second speed and a contraction of a ventricle of ahuman heart that is in blood flow communication with the blood pump. Thegenerated waveform drives the blood pump to generate a temporal rate ofchange of blood pressure that approximates a temporal rate of change ofblood pressure of a physiologic pulse. The generated waveform is furtherconfigured to produce a corresponding change in pump operating speed ata desired time. The second period of time is greater than the firstperiod of time.

In another general aspect, producing a pulsatile blood flow having arelatively low pressure portion and a relatively high pressure portionand having a rate of pressure change that mimics a rate of pressurechange of a natural physiologic pulse includes operating a continuousflow blood pump to produce a first blood flow rate through thecontinuous flow blood pump associated with the relatively low pressureportion of the pulsatile blood flow, operating the continuous flow bloodpump to produce a second blood flow rate through the continuous flowblood pump associated with the relatively high pressure portion of thepulsatile blood flow, and controlling the continuous flow blood pump toincrease a blood flow rate through the continuous flow blood pump fromthe first flow rate to the second flow rate to produce the rate ofpressure change that mimics the rate of pressure change of the naturalphysiologic pulse.

Implementations can include one or more of the following features. Forexample, operating the continuous blood flow pump to produce the secondblood flow rate can include operating the continuous blood flow pump ata first operating speed, and controlling can include operating thecontinuous blood flow pump at a second operating speed, the secondoperating speed being associated with a third blood flow rate, the thirdblood flow rate being greater than the second blood flow rate. Operatingthe continuous flow blood pump to produce the second blood flow rateincludes operating the continuous flow blood pump to produce the secondblood flow rate such that the relatively high pressure portion has aduration that is longer than a duration of the relatively low pressureportion. Repeating a cycle in which the duration of the relatively highpressure portion is greater than half of the duration of the cycle. Thecycle includes operating the continuous flow blood pump to produce thefirst blood flow rate, operating the continuous flow blood pump toproduce the second blood flow rate, and controlling the continuous flowblood pump to increase the blood flow rate. Operating the continuousflow blood pump to produce the second blood flow rate includes operatingthe continuous flow blood pump to produce the second blood flow ratesuch that the second blood flow rate has a predefined relationship withan average blood flow rate of the pulsatile blood flow. The second bloodflow rate is substantially equal to an average blood flow rate of thepulsatile blood flow. Controlling the continuous flow blood pump toincrease the blood flow rate includes controlling the continuous flowblood pump to increase the blood flow rate through the continuous flowblood pump from the first flow rate to the second flow rate such thatthe blood flow rate through the continuous flow blood pump overshootsthe second flow rate to produce the rate of pressure change that mimicsthe rate of pressure change of the natural physiologic pulse.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an implanted blood pump.

FIGS. 2-5 are diagrams illustrating pump speed patterns.

FIG. 6 is a diagram of a computer system.

DETAILED DESCRIPTION

With reference to FIG. 1, a left ventricular assist blood pump 100 isimplanted in a patient's body to assist or replace the patient's heart Hin pumping blood. Pump 100 has a housing 110 including an inlet cannula112 that extends into the left ventricle LV of the heart H. Connected tothe housing 110 is an outlet conduit 102 that conducts blood from theblood pump 100 to the patient's circulatory system. The blood pump 100can be a continuous flow pump, for example, a rotary pump. The bloodpump 100 can provide axial flow, centrifugal flow, or mixed axial andcentrifugal flow.

The blood pump 100 includes a stator 120 and a rotor 140. The rotor 140includes an impeller to move blood from the inlet cannula 112 to theoutlet conduit 102. For example, the blood pump 100 can be the pumpdescribed in U.S. Provisional Patent Application Ser. No. 61/375,504,filed Aug. 20, 2010, the entire contents of which are herebyincorporated by reference. In some implementations, the rotor 140 isseparated from an internal wall 115 of the housing 110 by a gap 108. Inuse, the gap is from approximately 0.1 millimeters to approximately 2.0millimeters. For example, in some implementations, the gap 108 isapproximately 0.5 millimeters during use. Additionally, in someimplementations, the rotor has a weight from approximately 5 grams toapproximately 50 grams. For example, in some implementations, the rotor140 has a weight of approximately 10 grams.

The rotation speed of the rotor 140 can be controlled to produce adesired blood flow rate. The desired blood flow rate can be selected toprovide a desired level of assistance to the patient's heart H. Forexample, the blood flow rate can be selected to partially assist theblood circulation function of the patient's heart H. Alternatively, theblood flow rate can be selected to substantially replace the bloodcirculation function of the patient's heart. The rate of flow of bloodfrom the inlet cannula 112 to the outlet conduit 102 is controlled, atleast in part, by controlling the rate of rotation of the rotor 140based on a direct relationship between the pump speed and the rate ofblood flow through the blood pump 100.

In addition to producing blood flow at a desired rate, a pulsatile bloodflow pattern may be desired. A pulsatile blood flow pattern includestime periods of relatively high blood flow rates and blood pressures andtime periods of relatively low blood flow rates and blood pressures.Such a pulsatile blood flow pattern may be desired to augment or replacea weakened pulse in patients, especially those whose native cardiacoutput is small compared to the volume flow rate of the blood pump.Additionally, a pulsatile blood flow pattern may be desired to produce aphysiologic response similar to that of a native pulsatile blood flowpattern and/or blood pulse pressure from a healthy heart. Thisphysiologic response may be markedly different than the response of ablood pump operating at a constant speed. While non-pulsatilecirculation can lead to certain physiologic, metabolic, and vasomotorchanges, the clinical relevance of pulsatility for VADs is unclear.Nevertheless, it is hypothesized that pulsatile circulation may reduceblood stasis in the ventricles, help exercise the aortic valve, improvewashing on the distal side of atherosclerotic lesions, increase coronaryand/or end organ perfusion, reduce the risk of ventricular suction,reduce the propensity for maladies related to reduced pulsatility, suchas arteriovenous malformations, and increase myocardial recovery.Further, it is expected that these phenomena do not require mimicking anative pulse waveform in its entirety. Rather, such may be accomplishedwith the techniques and waveforms described herein.

Importantly, various characteristics of the artificial pulse may differsubstantially from those of a physiologic pulse even while producing aresponse in the body that is similar to that caused by the physiologicpulse. Although with the multitude of potential clinical advantagesthere may be different aspects of a native pulse that mediatephysiologic response, it is generally understood that the dominantsource of dissipated energy that characterizes a meaningful pulse is thepressure wave generated at the start of cardiac systole. Accordingly,the artificial pulse described herein can include a relatively briefperturbation of a nature designed to produce such dissipated energy.

In some implementations, an artificial pulse cycle includes aperturbation period that simulates the pulse pressure that occurs at theleading edge of systole of a physiologic pulse. The perturbation periodcan include, for example, a period during which the blood pump 100 isoperated at a low speed, followed immediately by a period during whichthe blood pump 100 is operated at a higher speed. The artificial pulsecycle can also include a period longer than the perturbation periodduring which the pump 100 is operated at an intermediate speed, forexample, a speed maintained between the speeds realized during theperturbation period.

Operating the pump at the intermediate speed can contribute to a highoperating efficiency. The efficiency achieved can be greater than, forexample, the efficiency of a pump that only alternates between equalperiods of operation at a high speed and at a low speed. Typically, acontinuous flow pump operates with highest efficiency near the middle ofits rotational speed range. Therefore, it can be advantageous to operatesuch a pump at or near a mid-range speed for at least a portion of anartificial pulse cycle.

Some of the parameters that affect physiologic phenomena include pulsepressure and the rate of blood pressure change (dp/dt). For the bloodpump 100, for example, pulse pressure and time variation in bloodpressure are affected by the angular velocity of the rotor 140. Thus,the blood pump 100 can be selectively controlled to produce a pulsatileblood flow pattern, including a desired pulse pressure and/or a desiredrate of pressure change, by producing a pump speed pattern that includesa time period of relatively high rotor rotation speeds and a time periodof relatively low rotor rotation speeds. In some implementations, thepulse pressure produced by the blood pump 100 or produced by the bloodpump 100 and the patient's heart H in combination can be approximately10 mmHg or more, such as from approximately 20 mmHg to approximately 40mmHg.

For example, the blood pump 100 can be operated to produce a pump speedpattern 200, illustrated in FIG. 2. The pump speed pattern 200 includesa first portion 210 with high pump speed producing a relatively highblood pressure, and a second portion 220 with low pump speed producing arelatively low blood pressure. Additionally, the pulsatile blood flowpattern can include a transition between the first portion 210 and thesecond portion 220 that produces a desired rate of pressure change inthe patient's circulatory system, such as a rate of pressure change thatsimulates a natural physiologic pulse and that produces desiredphysiological effects associated with rate of pressure change. In someimplementations, the rate of pressure change produced by the transitionis, for example, between 500 to 1000 mmHg per second.

The first portion 210 and/or the second portion 220 of the pump speedpattern 200 can include multiple segments. In some implementations, thesegments each have predetermined durations. As also shown in FIG. 2, thefirst high speed portion 210 of the pump speed pattern 200 includes afirst segment 210 a and a second segment 210 b. In the first segment 210a, the rotor 140 is rotated at a first rotation speed ω1 for a firstperiod of time from a time T0 to a time T1. At the time T1, the rotationspeed of the rotor 140 is rapidly decreased from the first rotationspeed ω1 to a second rotation speed ω2, producing a stepped transition.The rotor 140 is rotated at the second rotation speed ω2 for a secondperiod of time from the time T1 to a time T2 during a second segment 210b of the first portion 210 of the pump speed pattern 200. At the timeT2, the rotation speed of the rotor 140 is decreased to a third rotationspeed ω3 for a third period of time from the time T2 to a time T4 duringthe second portion 220 of the pump speed pattern 200. This speeddecrease may be as rapid as the aforementioned speed increase, or moregradual to mimic pressure changes during native diastole.

In the pump speed pattern 200, the second rotation speed ω2 is a targethigh blood flow pump speed, and the first rotation speed ω1 is a desiredovershoot pump speed that is selected to increase the rate of change ofthe blood pressure during the first period. The first period of timefrom the time T0 to the time T1, during which the blood pump 100 isoperated at the first rotation speed ω1, is shorter than the secondperiod of time from the time T1 to the time T2, during which the bloodpump 100 is operated at the second rotation speed ω2. The first periodof time can be from approximately 0.01 seconds to approximately 1second. In some implementations, the first period of time isapproximately 0.05 seconds in duration. In some implementations, thefirst period of time can be approximately equal to, or greater than thesecond period of time.

Additionally, the duration of the first period can be selected toproduce a desired pulse pressure, i.e., the difference between bloodpressure before the speed change time T1 and during the time T1, and canbe selected independently of the duration of the second period of time.The first portion 210, including the first and second time periods fromthe time T0 to the time T2, is longer than the second portion 220. Insome implementations, the first and second time periods from the time T0to the time T2 can be shorter than, longer than, or substantially thesame duration as the second portion 220. For example, to increase theduration of pumping at the higher flow rate relative to pumping at thelower rate while still benefiting from the occasional pulse, it may beadvantageous for the first portion 210 to be longer than the secondportion 220. If desired, the speed of the blood pump 100 is increased tothe first rotation speed ω1 and the pump speed pattern 200 can berepeated. The pump speed pattern 200 can be repeated on a continuous ordiscontinuous basis, and the increase of rotation speed of the rotor 140is also sufficiently rapid to produce a desired rate of pressure change.

The concept of overshooting the rotation speed ω2 with a greater speed,such as rotation speed ω1, is based upon partly decoupling pulsepressure, i.e. the difference between the blood pressures before andafter the speed change, from the volume flow rate at the higher speed.Thus, target pulse pressures and volume flow rates can be attained atvarious flow conditions. Ideal values will vary with particular pumpdesign and requirements.

As shown in FIG. 2, the period 210 b can be longer than the period 210a. The period 210 b can also be longer than the portion 220. In someimplementations, the duration of the period 210 b is more than half ofthe duration of the pump speed pattern 200. For example, the duration ofthe period 210 b can be 60%, 70%, 80% or more of the duration of thepump speed pattern 200. As an alternative, depending on patient needsand pump characteristics, the duration of the period 210 b can be 50% orless of the duration of the pump speed pattern 200, for example, 40%,30%, 20% or less.

Operating the pump at the rotation speed ω2 during the period 210 b cancontribute to a high hydraulic efficiency during the pump speed pattern200. During the pump speed pattern 200, the pulse pressure generated ina patient's body is generally correlated to the change in pump rotationspeed, for example, the magnitude of the speed change between the speedsω3 and ω1 at time T4. Therefore, to simulate a pressure change thatoccurs at the beginning of systole of a physiologic pulse, a significantspeed differential between the rotation speeds ω3 and ω1 is generallydesired. The speed differential can be, for example, 1000 rpm, 2000 rpm,or more depending on the characteristics of the blood pump 100. Due tothe magnitude of the speed differential, one or both of the speeds ω3 toω1 may occur outside the range of highest operating efficiency of theblood pump 100.

The rotation speed ω2 can be a speed that results in a high hydraulicefficiency of the blood pump 100, for example, a speed near the middleof the operating range of the blood pump 100. During the pump speedpattern 200, the blood pump 100 can operate at the speed ω2 that resultsin high efficiency for a significant portion of the pump speed pattern200, contributing to a high efficiency. As described above, the bloodpump 100 can operate at the speed ω2 for more than half of the durationat the pump speed pattern 200. Thus the blood pump 100 can operate in ahighly efficient manner for the majority of the pump speed pattern 200and can also produce a pressure change that simulates the beginning ofsystole of a physiologic heart. Accordingly, some implementations of thepump speed pattern 200 can provide a higher efficiency than controlmodes that attempt to mimic all aspects of a native cardiac cycle.

The length of the period 210 b relative to the length of the pump speedpattern 200 can vary based on the frequency of the artificial pulse. Theduration of the period 210 a and of the portion 220, by contrast, can beindependent of the pulse rate. To produce the desired physiologicalresponse, a minimum duration for the period 210 a and the portion 220can be selected, for example, 0.125 seconds. The period 210 b can fillthe remainder of the pump speed pattern 200.

As an example, the pump speed pattern 200 can have a duration of onesecond, for a frequency of 60 cycles per minute. Given that the period210 a and the portion 220 have a combined duration of 0.125 seconds, theperiod 210 b can have a duration of 0.750 seconds, or 75% of the pumpspeed pattern 200. As another example, when the pump speed pattern 200has a duration of two seconds (and thus a frequency of 30 cycles perminute), the duration of the period 210 b can be 1.75 seconds, which is87.5% of the duration of the pump speed pattern 200.

In some implementations, the rotation speed ω2 is selected such that theoperation of the blood pump 100 at the rotation speed ω2 produces a flowrate that has a predetermined relationship relative to the average flowrate during the pump speed pattern 200. The flow rate during the portion210 b can be within a predefined range of the average flow rate, forexample, within 30% or within 10% of the average flow rate. The flowrate during the portion 210 b can be substantially equal to the averageflow rate.

Selecting the rotation speed ω2 to produce a flow rate that issubstantially equal to the average flow rate can facilitate a transitionbetween a pulsatile control mode and another control mode, such as acontinuous flow control mode. In some implementations, the blood pump100 operates at a particular constant speed for the greater part of thepump speed pattern 200. Operation at the constant speed can occurduring, for example, the period 210 b. By adjusting the speeds ω1 and ω3and duration of the period 210 a and of the portion 220, the averagepump volume flow rate can be tuned to substantially match an averagepump volume flow rate that would be realized in a different optionalsetting. Consequently, a clinician or patient can switch from anartificial pulse mode to another control mode in a manner that causesonly a small difference or no difference in average volume flow rate.This can provide a clinical advantage when the artificial pulse is aselectable option among at least one alternative, for example, aconstant speed option.

As an example, a speed set by a clinician for a constant speed mode canalso be utilized for a constant speed portion of an artificial pulsemode. The speed can be selected by the clinician to produce a desiredvolume flow rate through the blood pump 100 during the constant speedmode (e.g., during continuous flow or non-pulsatile operation of theblood pump 100). In the artificial pulse mode, the same selected speedcan be used as, for example, the rotation speed ωduring the period 210 bof the pump speed pattern 200. The speeds ω1, ω3 and the duration of theperiod 210 a and the portion 220 are calculated or chosen toapproximately balance the volume flow rate for the pump speed pattern200. For example, the reduced flow rate during the portion 220 canoffset the increased flow rate during the portion 210 a. As a result,the net volume flow rate during the pump speed pattern 200 cansubstantially match the volume flow rate during the constant speed mode.Thus in either the constant speed mode or the artificial pulse mode, thevolume flow rate can be approximately the same, permitting the clinicianto switch from one mode to another without affecting the volume flowrate. This can help avoid potentially dangerous conditions that couldoccur if switching from one mode to another resulted in sudden changesin flow rate. For example, a sudden decrease in volume flow rate couldcause acutely insufficient perfusion for the patient, and a suddenincrease in volume flow rate could cause ventricular suction andarrhythmia.

As mentioned above, the second portion 210 of the pump speed pattern 200can also include multiple segments. For example, as shown in FIG. 3, apump speed pattern 300 includes a first portion 310 that has a firstsegment 310 a and a second segment 310 b and the pump speed pattern 300includes a second portion 320 that has a first segment 320 a and asecond segment 320 b. During the first segment 310 a, from the time T0to the time T1, the blood pump 100 is operated at the first rotationspeed ω1. At the time T1, the speed of the blood pump 100 is reduced tothe second rotation speed ω2, and the blood pump 100 is operated at thesecond rotation speed ω2 for the second period of time from the time T1to the time T2. At the time T2, the speed of the blood pump 100 isreduced from the second speed ω2 to the third rotation speed ω3. Theblood pump 100 is operated at the third rotation speed ω3 for a thirdperiod of time from the time T2 to a time T3 during a first segment 320a of the second portion 320 of the pump speed pattern 300. At the timeT3, the speed of the blood pump 100 is increased from the third rotationspeed ω3 to a fourth rotation speed ω4, and the blood pump 100 isoperated at the fourth rotation speed ω4 during a fourth period of timefrom the time T3 to the time T4 during a second segment 320 b of thesecond portion 320 of the pump speed pattern 300. If desired, the speedof the blood pump 100 is increased to the first rotation speed ω1 andthe pump speed pattern 300 can be repeated. The pump speed pattern 300can be repeated on a continuous or discontinuous basis, and the increaseof rotation speed of the rotor 140 is also sufficiently rapid to producea desired rate of pressure change.

Similar to the concept of overshooting ω2 in pattern 200, the concept ofovershooting the rotation speed ω4 with a lower rotation speed, such asthe rotation speed ω3, is also based upon decoupling pulse pressure fromthe volume flow rate at the lower rotation speed ω4. Thus, the pumpspeed pattern 300 more completely decouples target pulse pressures andvolume flow rates than the pump speed pattern 200, and ideal values canbe attained, or more closely approximated, at various flow conditions.

While a single overshoot pump speed for a transition between pump speedsare illustrated and described with reference to FIGS. 2 and 3, multipleovershoot pump speeds for one or more transitions can be used. Forexample, FIG. 4 illustrates a pump speed pattern 400 that includesmultiple overshoot pump speeds for each transition. The pump speedpattern 400 includes a first portion 410 having a first segment 410 aand a second segment 410 b, and that includes a second portion 420having a first segment 420 a and a second segment 420 b. The firstsegment 410 a of the first portion 410 of the pump speed pattern 400includes a first step 431 during which the blood pump 100 is operated atthe first rotation speed ω1 to overshoot the target pump speed ω2 and asecond transition step 433 during which time the blood pump 100 isoperated at a fifth speed ω5 to transition from the first rotation speedω1 to the second rotation speed ω2. Similarly, the first segment 420 aof the second portion 420 includes a first step 441 during which theblood pump 100 is operated at the third rotation speed ω3 and a secondsegment 443 during which the blood pump 100 is operated at a sixth speedω6 to transition between the third speed ω3 and the fourth rotationspeed ω4. If desired, the speed of the blood pump 100 is increased tothe first rotation speed ω1 and the pump speed pattern 400 can berepeated. The pump speed pattern 400 can be repeated on a continuous ordiscontinuous basis, and the increase of rotation speed of the rotor 140is also sufficiently rapid to produce a desired rate of pressure change.

The concept of creating multiple stepwise rotation speed changes isbased upon producing the physiologic response that is similar to thatproduced during human cardiac systole and diastole. This is distinctfrom mimicking the nature of a native pulse waveform in its entirety. Asdescribed above, greater hydraulic efficiency can often be achieved byavoiding imitation of the physiologic pressure waveform over the pulsecycle. It was previously mentioned that an artificial pulse offers amultitude of potential clinical advantages. For some or all of thesepotential clinical advantages, the benefit of closely matching theenergy dissipated during a healthy native pulse varies. To the extentthat close matching facilitates achieving these potential clinicaladvantages, the additional complexity of pattern 400 may be warranted.

In contrast to the stepped or discontinuous transitions discussed abovewith respect to FIGS. 2-4, smooth or continuous transitions may be usedin place of, or in combination with, stepped transitions betweendifferent pump operation speeds. For example, smooth transitions areillustrated in the pump speed pattern 500 of FIG. 5. The pump speedpattern 500 includes a first portion 510 and a second portion 520. Thefirst portion 510 includes a first segment 510 a during which the speedof the pump 100 is decreased gradually, at a strategically-selectedrate, from the first rotation speed ω1 to the second rotation speed ω2from the time T0 to the time T1. The selected rate of pump speeddecrease can be, for example, a particular linear rate or a particularnon-linear rate. During the second segment 510 b of the first portion510, from the time T1 to the time T2, the blood pump 100 is operated atthe second rotation speed ω2. Similarly, the second portion 520 includesa first segment 520 a during which the speed of the blood pump 100 isincreased gradually, at a strategically-selected rate, from the thirdrotation speed ω3 to the fourth rotation speed ω4 from the time T2 tothe time T3. During the second segment 520 b of the second portion 520,from the time T3 to the time T4, the blood pump 100 is operated at thefourth rotation speed ω4. If desired, at time T4, there is a stepincrease in the rotation speed of the rotor 140 can be rapidly increasedto the first rotation speed ω1, and the pump speed pattern 500 isrepeated.

The concept of creating multiple speed changes at astrategically-selected rate is based upon producing the physiologicresponse that is similar to that produced during human cardiac systoleand diastole. For example, if very accurate matching of energydissipation during a human pulse is necessary, the additional complexityof pattern 500 may be warranted.

The pump speed pattern 500 illustrates the difference between steppedtransitions discussed above with respect to pump speed patterns 200-400,produced by rapidly changing the rotation speed of the rotor 140, andthe gradual transitions of the first segment 510 a of the first portion510 and the first segment 520 a of the second portion 520 of the pumpspeed pattern 500. Such gradual transitions can be included, forexample, to mimic pressure changes exhibited during native diastole, asmay be achieved by the gradual transition of the first segment 510 a ofthe first portion 510 of the pump speed pattern 500. In someimplementations, one or more of the rotation speed decreases of a pumpspeed pattern can be gradual transitions. For example, a pump speedpattern can include a gradual decrease in rotation speed from the firstrotation speed ω1 to the third rotation speed ω3 and a steppedtransition from the third pump speed ω3 back to the first rotation speedω1. Various combinations of stepped and gradual transitions can beincluded in a pump speed pattern to produce a desired arterial pressurewave form, or other desired physiologic effect. Additionally, the typeof transition between rotation speeds can affect power consumption ofthe blood pump 100, and the pump speed pattern can be selected based, atleast in part, on power consumption considerations.

For all the pump speed patterns discussed it should be appreciated thatalthough rotor speed is the technological parameter utilized to impartan artificial pulse, any physiologic effect is related to theconsequential pressure and flow patterns, including pulse pressure, themaximum time variation in rate of blood pressure change (dp/dt), and thelike. Rotor speed is not intrinsically physiologically meaningful. Thehuman vascular system naturally dampens the native pulse produced by theheart, and it will do the same for an artificial pulse produced asdescribed. The invention describes a utilitarian combination of factorsthat result in a physiological meaningful pulse. Thus, the pump speedpatterns 200-500 described above are exemplary combinations ofparameters that result in a physiologically meaningful pulse.

In use, the pump speed patterns 200-500 can be generated by a controllerthat is configured to generate an electrical drive signal to operate theblood pump 100. For example, the controller can include a computersystem 600, shown in FIG. 6, that outputs an electrical current tooperate the blood pump 100. In order to produce the pump speed pattern200 described above, the controller outputs a first electrical currentfrom the time T0 to the time T1. At the time T1, the controller reducesthe output electrical current to a second current that is lower than thefirst electrical current, and outputs the second electrical current fromthe time T1 to the time T2. At the time T2, the controller reduces theoutput electrical current from the second current to a third current,and outputs the third electrical current from the time T2 to the timeT4.

The computer system 600 includes one or more processors 610, memorymodules 620, storage devices 630, and input/output devices 640 connectedby a system bus 650. The input/output devices 640 are operable tocommunicate signals to, and/or receive signals from, one or moreperipheral devices 660. For example, a peripheral device 660 can be usedto store computer executable instructions on the memory modules 620and/or the storage devices 630 that are operable, when executed by theprocessors, to cause the controller to generate a waveform to controlthe operation of the pump 100 and produce a pump speed pattern, such asthe pump speed patterns 200-500.

Additionally, the controller can include a sensor that provides a signalthat indicates activity of the heart H. For example, the controller caninclude a sensor that provides a signal indicative of power consumptionof the blood pump 100. The signal can be used to determine when the leftventricle LV contracts. For example, the power consumption of the bloodpump 100 may, for a given operating speed, increase as the leftventricle LV contracts. Based on the determined heart activity, thecontroller can adjust the generated control waveform. For example, thecontroller can automatically adjust the timing and duration of the firstportion 210 and the second portion 220 of the pump speed pattern 200such that the first portion 210 approximately coincides with acontraction of the left ventricle LV. The pump 100 is controlled suchthat the time T0 approximately coincides with a beginning of acontraction of the left ventricle LV and the time T2 approximatelycoincides with an end of the contraction of the left ventricle LV. Thetime T4 approximately coincides with a beginning of a subsequentcontraction of the left ventricle LV. Thus, the durations of the variousportions and/or segments of the pump speed patterns described above canbe changed individually or collectively for one or more repetitions ofthe pump speed patterns. Using these techniques, the controller cansynchronize the pulsatile operation of the blood pump 100 with thenatural physiologic pulse of the heart H.

Alternatively, the controller can generate the control waveformindependently of the activity of the heart H and/or to operate inopposition to the activity of the heart H, such as where the firstportion 210 occurs during left ventricular relaxation. Similarly, thecontroller can generate a control waveform that includes a distinctlynon-physiologic pulse rate, such as fewer than 40 high-pressure periodsper minute, and the waveform can be generated independently of nativeheart function. In some examples, the blood pump 100 can be operated toproduce distinctly physiologic pulse rates, such as between 50 and 110high-pressure periods per minute, and can be controlled dependently orindependently of heart function.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications may be made without departingfrom the spirit and scope of the claimed invention. For example, thepump speed patterns described above can be used with various types ofblood pumps, including axial flow blood pumps and centrifugal flow bloodpumps. Similarly, the rotors of blood pumps used to produce pulsatileblood flow patterns as described above may beelectromagnetically-suspended, hydraulically-suspended,mechanically-suspended, or combinations thereof. The rotors may alsopartially be passively magnetically-suspended. However, the effect of anartificial pulse may most accurately be simulated by a pump in which therotor is electromagnetically suspended, with or without partial passivemagnetic suspension, because in general, other things being equal,electromagnetic suspension yields a high degree of responsiveness of therotor to speed change inputs. For example, mechanical bearingsassociated with mechanical suspension and/or very narrow rotor clearancegaps associated with hydraulic suspension hinder rapid acceleration ofthe rotor compared to similar pumps that employ electromagneticsuspension. Additionally, while the pump speed patterns described abovehave been described with regard to a measure of angular velocity, thepump speed patterns can be produced with regard to one or more differentmeasures of pump speeds. Additionally, there may be a delay between achange in drive signal generated by the controller and a change inoperating speed of the blood pump. Thus, the controller can be operatedsuch that changes in the output drive signal are effected at a time toproduce a corresponding change in pump operating speed at a desiredtime, such as a time that approximately coincides with selected activityof the heart.

In some implementations, the pump speed patterns 200-500 can includeadditional portions or segments during which the blood pump is operatedat other speeds. For example, at desired times, the blood pump can beoperated to produce a pump speed pattern that produces a desiredphysiologic effect, such as opening or closing the aortic valve. Suchoperation of the blood pump can interrupt a generally continuousrepetition of a selected one or more of the pump speed patternsdescribed above, or others, including an indefinite period of constantspeed, and a selected pump speed pattern can be resumed after thedesired physiologic effect has been produced. The pump speed patterns200-500 can also include different portions or segments. For example,the second segment 210 b of the first portion 210 of the pump speedpattern 200 can include multiple pump speeds. Similarly, the transitionsbetween pump speeds, such as the reduction in pump speed from the firstrotation speed ω1 to the second rotation speed ω2, can include constant,variable, exponential, combinations thereof, or other rate of speedchange over time such that the transition, such as the first segment 510a of the first portion 510 of the pump speed pattern 500, is linear,curvilinear, parabolic, logarithmic, sinusoidal, stepped, orcombinations thereof.

In some implementations, one or more of the pump speed changes in thepump speed patterns 200-500 can be monotonic. A transition from onespeed to another may occur gradually over a period of time, yet changedirectly from one speed to another. For example, to decrease a pumpspeed from a first rotational speed to a second rotational speed, thecontroller can reduce the pump speed without causing an interveningperiod of increasing pump speed. Similarly, the transition from thefirst rotational speed to the second rotational speed can occur withoutoperating the pump above the first rotational speed during thetransition.

Additionally, a blood pump can be operated according to a pump speedpattern that is selected according to a pump power consumption rateassociated with the pump speed pattern, a pump efficiency associatedwith the pump speed pattern, a blood flow rate associated with the pumpspeed pattern, and/or a rate of blood pressure change associated withthe pump speed pattern. For example, in a first mode, the controller canbe operated to produce a pump speed pattern that produces a desired rateof blood pressure change. When a low power condition is detected, thecontroller can be switched to a power-saving mode to produce a pumpspeed pattern that has a low power consumption rate, even if the desiredrate of pressure change is not produced in the power-saving mode.

As mentioned above, in some implementations, the blood pump 100 can beused to assist a patient's heart during a transition period, such asduring a recovery from illness and/or surgery or other treatment. Inother implementations, the blood pump 100 can be used to partially orcompletely replace the function of the patient's heart on a generallypermanent basis, such as where the patient's aortic valve is surgicallysealed.

The subject matter and the functional operations described in thisspecification can be implemented in digital electronic circuitry, intangibly-embodied computer software or firmware, in computer hardware,including the structures disclosed in this specification and theirstructural equivalents, or in combinations of one or more of them. Thesubject matter described in this specification can be implemented as oneor more computer programs, i.e., one or more modules of computer programinstructions encoded on a tangible non transitory program carrier forexecution by, or to control the operation of, data processing apparatus.The program carrier can be a computer storage medium, for example, amachine-readable storage device, a machine-readable storage substrate, arandom or serial access memory device, or a combination of one or moreof them, as described further below. Alternatively or in addition, theprogram instructions can be encoded on an artificially generatedpropagated signal, e.g., a machine-generated electrical, optical, orelectromagnetic signal, that is generated to encode information fortransmission to suitable receiver apparatus for execution by a dataprocessing apparatus.

The term “data processing apparatus” encompasses all kinds of apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include special purpose logic circuitry, e.g., an FPGA(field programmable gate array) or an ASIC (application specificintegrated circuit). The apparatus can also include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them.

A computer program (which may also be referred to or described as aprogram, software, a software application, a module, a software module,a script, or code) can be written in any form of programming language,including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A computer program may, butneed not, correspond to a file in a file system. A program can be storedin a portion of a file that holds other programs or data, e.g., one ormore scripts stored in a markup language document, in a single filededicated to the program in question, or in multiple coordinated files,e.g., files that store one or more modules, sub programs, or portions ofcode. A computer program can be deployed to be executed on one computeror on multiple computers that are located at one site or distributedacross multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable computers executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Computers suitable for the execution of a computer program can include,by way of example, general or special purpose microprocessors or both,or any other kind of central processing unit. Generally, a centralprocessing unit will receive instructions and data from a read onlymemory or a random access memory or both. The essential elements of acomputer are a processing unit for performing or executing instructionsand one or more memory devices for storing instructions and data. Acomputer can also include, or be operatively coupled to receive datafrom or transfer data to, or both, one or more mass storage devices forstoring data, e.g., magnetic, magneto optical disks, or optical disks.However, a computer need not have such devices. Moreover, a computer canbe embedded in another device, e.g., a pump, a pump controller, or aportable storage device, e.g., a universal serial bus (USB) flash driveor other removable storage module, to name a few.

Computer readable media suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks,e.g., internal hard disks or removable disks; magneto optical disks; andCD ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

Accordingly, other embodiments are within the scope of the followingclaims.

1. A method of controlling an implantable blood pump, the methodcomprising: operating the implantable blood pump in a first pump speedpattern to provide a pulsatile operational mode; detecting a low powercondition; transmitting, based on the detection of the low powercondition, a signal to the implantable blood pump to transition theimplantable blood pump from the first pump speed pattern to a secondpump speed pattern, the second pump speed pattern having a lower powerconsumption rate than the first pump speed pattern.
 2. The method ofclaim 1, wherein the first pump speed pattern is associated with a firstblood flow rate, and the second pump speed pattern is associated with asecond blood flow rate different than the first blood flow rate.
 3. Themethod of claim 1, wherein the first pump speed pattern is associatedwith a first rate of blood pressure change, and the second pump speedpattern is associated with a second rate of blood pressure changedifferent than the first rate of blood pressure change.
 4. The method ofclaim 1, wherein operating the implantable blood pump comprises: (a)operating the implantable blood pump at a first speed for a first periodof time; (b) reducing the speed of the implantable blood pump from thefirst speed to a second speed; (c) operating the implantable blood pumpat the second speed for a second period of time; (d) reducing the speedof the implantable blood pump from the second speed to a third speed;(e) operating the implantable blood pump at the third speed for a thirdperiod of time; and repeating steps (a)-(e).
 5. The method of claim 4,further comprising transmitting a second signal to the implantable bloodpump to change the first speed, the second speed and/or the third speed.6. The method of claim 4, further comprising transmitting a secondsignal to the implantable blood pump to change the first period of time,the second period of time, or the third period of time.
 7. A method ofcontrolling an implantable blood pump, the method comprising: operatingthe implantable blood pump in an artificial pulse mode for a firstperiod of time; transmitting a first signal to the implantable bloodpump to transition the implantable blood pump from the artificial pulsemode to a constant speed mode; operating the implantable blood pump inthe constant speed mode for a second period of time; and transmitting asecond signal to the implantable blood pump to transition theimplantable blood pump from the constant speed mode to the artificialpulse mode; operating the implantable blood pump back in the artificialpulse mode.
 8. The method of claim 7, wherein a net volume flow rate ofthe implantable blood pump during the artificial pulse mode matches thenet volume flow rate of the implantable blood pump during the constantspeed mode.
 9. The method of claim 7, further comprising receiving auser set speed for operating the implantable blood pump in the constantspeed mode.
 10. The method of claim 9, wherein operating the implantableblood pump in the artificial pulse mode comprises: (a) operating theimplantable blood pump at a first speed for a first speed period; (b)reducing the speed of the implantable blood pump from the first speed toa second speed; (c) operating the implantable blood pump at the secondspeed for a second speed period; (d) reducing the speed of theimplantable blood pump from the second speed to a third speed; (e)operating the implantable blood pump at the third speed for a thirdperiod of time; and repeating steps (a)-(e).
 11. The method of claim 10,wherein the second speed of the artificial pulse mode is set based onthe user set speed for operating the implantable blood pump in theconstant speed mode.
 12. The method of claim 11, wherein the secondspeed of the artificial pulse mode is equivalent to the user set speedfor operating the implantable blood pump in the constant speed mode. 13.The method of claim 12, wherein the first speed, the third speed, thefirst period of time, and the third period of time of the artificialpulse mode are calculated to provide a volume flow rate associated withthe artificial pulse mode that matches a volume flow rate associatedwith the constant speed mode.
 14. An implantable blood pump system, thesystem comprising: an implantable blood pump configured to supplement orreplace a pumping function of a heart, the implantable blood pumpoperable in a first pump speed pattern and a second pump speed pattern;a controller coupled with the implantable blood pump and configured toreceive a first input, and in response to receiving the first input, totransmit a signal to the implantable blood pump to transition fromoperating in the first pump speed pattern to operating in the secondspeed pattern.
 15. The implantable blood pump system of claim 14,wherein the first input is indicative of a low power condition of theimplantable blood pump system.
 16. The implantable blood pump system ofclaim 15, wherein the second pump speed pattern has a lower powerconsumption rate than the first pump speed pattern.
 17. The implantableblood pump system of claim 16, wherein the first pump speed patternprovides a pulsatile operational mode.
 18. The implantable blood pumpsystem of claim 14, wherein the controller is further configured toreceive a second input, and in response to the second input, to transmita signal to the implantable blood pump to transition from operating inthe second pump speed pattern to operating in the first pump speedpattern.
 19. The implantable blood pump system of claim 18, wherein thefirst pump speed pattern comprises an artificial pulse mode and thesecond pump speed pattern comprises a constant speed mode.
 20. Theimplantable blood pump system of claim 19, wherein the controller isfurther configured to receive a user input of a set speed for operatingthe implantable blood pump in the constant speed mode.
 21. Theimplantable blood pump system of claim 18, wherein the first and secondinputs are user commands.